Building a comprehensive test bench
Date Engine type Pull Weight P/W ratio Max. Pull oz.
9/1/13 Atlas SD60 1.75 4
oz. VA VA VA Min Mid Max .4375
11 .3
Performance log Wheel slip 11.2 .28
12 .5 12 52 90 Stall Scale speed
creasing the throttle and noting how many ounces of pull are shown on the balance scale. At maximum pull, before wheel slip, note it along with the voltage or throttle setting at that point. Then apply more throttle until wheel slippage occurs, and note the readings at that point. Third, while wheels are slipping, push down momentarily on the engine until the wheels stall, still advancing the throttle until maximum voltage (and amps, if you’re recording them) are recorded. Last, weigh the engine on the other scale, and divide the ounces of pull by the ounces of weight for a simple measure of pulling effectiveness. You might want to keep a log for
your roster. There’s a sample included with this article. It can come in handy if an engine becomes balky at some time to compare its performance to that of a previous measurement. It’s also a good idea to test and record the results for a new engine, and then again after it’s broken in. To test rolling stock, place it at the top of the ramp and release it. If it doesn’t roll down by itself, place it in bad-order. If it rolls down the ramp on its own, let it coast to a stop and meas- ure how far it went along the adjacent ruler. You can develop your own stan- dards for how far a car must roll to be acceptable on your layout. Cars should be weighted; use NMRA Recommended
Practice 20.1–see
The coupler height of rolling stock is checked with the height gauge (top). Similarly, the trip pin height needs to be tested (above). This should be done for locomotives, too.
Last, you’ll need to measure the en- ergy being applied to the locomotive from the power supply. For d.c., you’ll want to measure volts, and possibly amps. Cheap test meters that do both (but require re-connecting the leads between parallel for voltage and serial for amps) can be had for under $10.00, or you can use separate meters to measure both simultaneously.
For
DCC, the easiest approach is to use the setting on your throttle (percent of full throttle) as a relative measurement. Alternatively, you can use one of the
72
Using the lab Place an engine on the engine test
track and couple it to the yoke car. Throttle it up, moving it to the right, in-
relatively new DCC meters on the mar- ket that test a.c., d.c. and DCC, but these are more expensive (about $50.00 to $100.00). Note also that many of today’s DCC decoders will op- erate on d.c. as well, so you can do the volt/amp tests on DCC, and the speed tests on d.c. with the throttle settings as the key measurement.
www.nmra.org/standards/sandrp/ rp-20_1.html. This site specifies what a car should weigh based on its scale and length. Cars weighted to this will generally run a lot more trouble-free than if not. Quarter-ounce automobile wheel balancing weights with self- sticking adhesive backs are great for weighting cars. For both engines and rolling stock,
check their coupler height, trip pin height, and wheel gauge. Be sure to bad- order anything not meeting the appro- priate standard and get it corrected be- fore allowing it back on the layout. You can calculate your locomotive’s minimum, mid-point and maximum scale speeds on your layout and record them in the log. Another way to have fun with the test lab is to take it to meetings or shows to stage pulling con- tests, or to demonstrate standards to your organization. You can build a whole clinic around it.
SEPTEMBER 2013
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